Biomedical subjects
Publications and source records attributed to R S Bridges.
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The relationship among plasma progesterone, number of corpora lutea, and foetal number was assessed in Rockland-Swiss albino mice. While number of corpora lutea and foetal number were significantly correlated, neither was related to plasma progesterone level. This finding in the mouse is similar to results reported in the rabbit.
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The effects of suckling and LH upon serum progesterone levels in lactating hamsters were investigated. Diurnal rhythms in serum levels of progesterone and LH occur throughout lactation in the hamster and these levels are normally higher between 15.00 and 17.00 than between 8.00 and 12.00 (lights on 6.00-20.00). Hamsters injected with 10 mug of LH at 8.00 on day 9 of lactation had higher levels of serum progesterone 2 h after injections than did vehicle-injected controls. Suckling was also found to induce an increase in serum progesterone concentrations. 30 min of suckling from 10.30 to 11.00 on days 10 or 11 of lactation resulted in increased serum levels of progesterone and prolactin, but had no measurable effect upon serum LH levels in animals bled at 11.00. However, suckling for 30 min from 15.00 to 15.30 had no effect upon serum progesterone levels, although it did result in increased titers of both serum LH and prolactin at 15.30. Ovariectomy on day 7 of lactation resulted in lowered levels of serum progesterone at 11.00 on day 11 of lactation and abolished the suckling-induced increase in serum progesterone concentrations. These findings suggest that in the lactating hamster (1) suckling bouts stimulate progesterone secretion from the ovaries, and (2) the diurnal rise in serum progesterone levels is stimulated in part by the increase in serum levels of LH.
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The involvement of the ovaries during late pregnancy in the rat upon serum prolactin was investigated. Ovariectomy on day 17 or day 21 of pregnancy prevented the dramatic rise of prolactin found in sham-ovariectomized animals between days 21 and 23 of pregnancy. While animals ovariectomized on day 17 of pregnancy failed to carry viable fetuses beyond day 19 of pregnancy, rats ovariectomized on day 21 of pregnancy had viable pups in utero on day 23 of pregnancy. These data suggest that the rise in serum prolactin during late pregnancy is stimulated by ovarian factors.
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High levels of mu opioid receptor activation during the postpartum period result in the disruption of ongoing maternal behavior. The role of physiological levels of endogenous opioids on the mediation of maternal behavior in postpartum females, however, has not been closely examined. The purpose of the present experiments was to examine the function of endogenous opioids during early and mid-lactation by treating postpartum females with the opioid antagonist naloxone and monitoring their behavioral interactions with pups. Although this treatment did not lead to any qualitative differences in the maternal behaviors measured (pup retrieval and grooming, nest building, grouping of pups, or crouching over pups), there was a quantitative difference in the amount of time the females spent with pups on the nest and actively nursing pups. Naloxone, given either systemically or centrally (intracerebroventricularly), resulted in prolonged nursing and nesting bouts. This effect, however, was only observed during the early lactation time point (postpartum days 5-7). Females tested later in lactation (postpartum days 10-12 or 12-14) did not display the increased nursing or nesting bouts in response to the antagonist. These data indicate that central opioids play a role in the duration of nursing bouts during early lactation.